Among the best modern clocks are those which employ long-lived ground-state hyperfine transitions of mercury (Hg) ions to achieve stability and accuracy levels exceeding 10−15 (see e.g. J. D. Prestage et al, “Atomic Clocks and Oscillators for Deep-Space Navigation and Radio Science,” Proceedings of the IEEE, vol. 95, pp. 2235-2247, November 2007). This Hg ion clock is relatively large and bulky with a physics package which occupies about 1000 cubic centimeters (cc), and with an overall weight of the Hg ion clock being about 2-3 kilograms (kg). Further significant reductions in the size, weight and electrical power for the Hg ion clock are hampered by the requirements for ion shuttling and for the use of a 202Hg discharge lamp to provide deep ultraviolet (UV) radiation at 194 nanometers (nm) for optical pumping of 199Hg+ ions.
There is a current need for ion clocks (also referred to herein as ion frequency standards) which are about 100 times smaller than the Hg ion clock with a commensurate reduction in weight and required electrical power. Such small-size ion clocks have applications for use in nano satellites and unmanned aerial vehicles (UAVs).
The ion frequency standard of the present invention provides an advance in the art by providing an ion clock which operates using ytterbium (Yb) ions in a size, weight and electrical power requirement which are significantly less than those required for conventional Hg ion clocks.
The ion frequency standard of the present invention also utilizes a permanently-sealed vacuum package (also termed a vacuum housing) wherein the Yb ions are generated and isolated in an octupole ion trap without the need for any shuttling of the Yb ions.
Microwave radiation for the ion frequency standard of the present invention can be generated using an acoustic oscillator which can comprise a film bulk acoustic wave (FBAR) oscillator, a microresonator oscillator or an acoustic bandgap (ABG) oscillator. These acoustic oscillators are compact and rugged, and require relatively low electrical power to generate the microwave radiation.
Optical sources and detectors for the ion frequency standard of the present invention can be located on a common substrate to reduce the size, weight and electrical power requirements for these components which are needed for optical interrogation of the Yb ions.
These and other advantages of the present invention will become evident to those skilled in the art.